scuzzo

this bike is not ment to be a lamp!
ok so my prized litespeed. dream bike, white whale, bucket list kinda deal has developed a crack,, ick.. after exploring all my options..

1. make a lamp out of it... no... not gonna happen!

2. send it back to litespeed for a tube ectomy... cut out the down tube and replace... huge coin.. for this deal... near the price a new frame..

3. have it done local.. by this fellow that does aero space welding for nasa contractors and such... this will be at most 100 bucks but he pitched a fig of closer to 40.. will do the fish scale. row of nickel kinda finish weld..

i talked with the guy and he has a real passion for the work seems to know his stuff.. was an instructor in college... explained to me how he would back shield the weld.. to keep contamination.. out.. and seemed like just a really solid cat ..


now.. here is the bike in question... and im not sure how this crack showed up... just one day.... what is that creak sound? the bike rides fine but if this thing propagates... not cool.. so im going to have it welded and see if the stress crack is arrested... or it pops up on the other side of the tube... but the thing that surprises me is how the crack is arrow straight.. like some one took a straight edge and ran an exacto on it... i have looked at the titanium frame grave yards on the web and non look quite like this crack in a frame... i checked and the crack did not extend to the weld... took a pick and checked the rest of the frame and its all smooth... well anyway.. will be taking the frame in friday or nextweek... hope it comes out ok...


litespeed vortex 2007

TiHabanero

Wow. I wonder how that started. It looks like the tube is square with rounded corners and sits like a diamond at the weld joint. Is this correct?

Does the crack start in the weld or does it start at the edge of the weld?

unterhausen

it would most likely start in the heat affected zone near the weld, unless there is something at the weld that would cause a stress riser. Fatigue cracks in ductile metals are usually pretty straight in cases like this, that doesn't surprise me at all. i think most cracks you see on Ti bikes are on round tubes, they are going to be different.

Not sure a weld repair is going to last too long, but I suppose it's worth a try.

scuzzo

mikeread

Could you have the crack welded up and then a gusset welded over the top. Belt and braces.

unterhausen

"gussets tell the frame where to crack"

I first heard of this problem from a friend who was trying to patch a crack in an airplane bulkhead. They tested it, and it just cracked around the patch because all the deformation was being taken up by the material around the patch.

mikeread

If it were thin, long and tapered would that still be the case?

It would just be like the point on a lug and could be filed/tapered as thin as you like to minimise any changes in section.

unterhausen

yes, it would. Lugs can cause cracks. That's why we use butted tubing. I have the remnants of a head tube on my desk. I replaced it, there was a crack around the outline of the lug. It was really hard to see from the outside, but you could see the outline of the lug on the inside.

It was a really nice frame too, the paint changes color depending on the light conditions.

79pmooney

Those square tubes never passed my "eyeball engineering" test. Always looked to me like a problem waiting to happen. That bottom corner is one of the most stressed area in the diamond when you come down hard from a jump (tension) or either hit a pothole or the brake hard (compression). On top of that, the best shape for torsional stiffness and strength is a tube.

Really, a finite elements analysis (FEM) needs to be done with a really good simulated loads that reflect reality. Maybe they ran a lesser FEM and this looked good, but an engineer should also be able to step back and ask "does this make sense?"

I wouldn't trust a weld there for a second. (Well, maybe the first hundred miles.) But I;d be thinking "this weld has added additional stresses to this area. Given that tube shape , am I OK with that?"

To add to that is my concern about the location. If it were to fail, the front wheel will no longer be rigidly attached to the frame and the job of supporting the front end gets passed to the top tube; a job no one ever dreamed it would see. THis wold be ging through my mind eeery time I went downhill.

Ben

fietsbob

yup , need a Ti welder , to do that ...
Ti Cycles is in the woods just west of Portland Oregon. they do that..

Perhaps (general metal working)
Double that section, after crack end stopper drilling it
then welding it up. and then doubling it.
and add triangular braces between the down and head tubes.



....

scuzzo

decision made, Moderator please close thread..
thankyou